Separate magnetization of magnetic amplifiers



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s m z w E M H B O I n R n. m m NCJ YG 1 4 EM l. Y M 7 \l. B AF2 O 2D. RN c LS .O 8 P AI D M T OA .A d RZ e lc I l T i I m F 8T, G O.N m E am E. M ow L m um S T N O C v.. m. E .masi 0H .F5550 25o June 3o, 1953 x Patented June 30, 1953 UNITED LSTATES ATENT OFFICE SEPARATE MAGNETIZATION OF MAGNETIC AMPLIFIERS 4 Claims.

This invention relates in general to saturacle core reactors and in particular `to 2 reduction of the residual magnetizing current or amplier.

Magnetic amplifiers have been number of years during a greater I oi wille'.

de. Tn primary reason for the virtual discarding nl. netic amplifiers was the belief that tirer amplifiers were far superior -u all respe consequently thermionic amp., ahead of magnetic Vacuum tubes are, however, e component in certain in warfare equipment, especially wand ruggedness are essential. brought out late in the last wh re evident that magnetic amplifiers ccnld be used to good advantage in many places wh ,re tubeswere previously thought to 'ce Developments in other electrical nele-s p @dus high permeability magnetic alloys 'cti/pe rectiers; materials that could be applied with great advantage to magnetic amplifier techniques to enhance the present day development of magnetic amplifiers.

In the present day electrical magi J ampliiiers rind utility a sensitive robust sal vanomet r; a pre-amplifier for an electronic e. plier when the incoming signal is direct current thereby functioning as a .mfi.. C?. convert-e1 as a mixing device and amplifier s tem; speed and frequency ins rumeni', amplifiers; to drive and control th n portance to drive a motor at a sp' on the value of the input signal. for magnetic amplifiers are, oi course,

The magnetic ampliier, however, is in a still in the developmental stage since all of its capabilities are not :fully appreciated and further known magnetic amplifiers have shortcomings and limitations that also require further development. One of these limitations is the problem confronted with the performance ability versus expense of the cores with respect to their com position and structure.

In the iield of magnetic amplifiers, for of such limitation, the most commonly used core structure is the shell type iron, or as is usi known the three legged reactor. With this and other commonly used cores there generally the problem oi the introduction of gap. Even a small air gap in the magnetic circuit will reduce the A. C. permeability greatly and sec. 266) a Waste a great deal oi polarizing ability. The troduction of a gap introduces a nigh residual magnetizing current which when @owing through the load, masks the eects of the control current. This problem is especially serious when the ma netic ampliiier is employed in a circuit where it is essential to have no current flow when no con trol Voltage is applied, which is not the case ii a residual magnetizing current exists.

A major problem then, in the design of mag netic amplifiers, is to provide a core with no air gap. The solution to this problem has not been met with a great deal oi su.. It been found that the type of cere whi i es least air gap is the toroidahtype core consisting of a continuous strip of alloy steel. toroidal1 type core, however, has also proven to have a serious disadvantage i. e., the extreme diiiculty encountered in the winding oi 'the coils ther This winding process is extremely complex often by hand and quite expensive for a prod tion basis.

coming the above mentioned undesirable offer or" air gaps encountered through the ci co Y ventional type of cores. The soli. on of this problem permits the use of well. known t cores with the winding of the coils t'ne on fly conventional techniques. In other we present invention solves the problem of au gaps in cores by counteracting the above inenticned residual magnetizing current,

lt is accordingly an object or the presec verition to provide an improved ner of inexpensive construction,

A further object of the present invern-.ion provide a magnetic amplifier using the tional type of cores, but nevertheless free of the disadvantages normally therein.

Another object of the present reduce to substantially aero qu' rent ow through a magetic ampli'ier.

Further objects and attainments of the pr Fig. 2 illustrating a physical relations... windings. v

Fig. 4 shows a series of output current vs. control current curves both of a conventional netic amplifier and of a magnetic amplier cmploying the present invention.

In accordance with the spirit and scope of the present invention means are incorporated in a magnetic amplier to counteract the high residual magnetizing current, as previously explained, caused principally by air gaps that exist in the conventional. type or magnetic core. The high residual magnetizing current that masks the effects of the control current is counteracted by causing an additional magnetizing current of equal ampere-turns Value to flow through a separate coil not necessarily connected electrically to the output circuit.

Brieily, this separate coil comprises a pair of windings positioned in adjacent relationship to the load winding and having a relatively few number of turns. This separate winding is energized with an amount of alternating current determined by the value necessary for normal magnetization.

The operation of magnetic amplifiers is well known in the art and is the subject of many publications. However, to assist in understanding the function of the present invention it may be best to give a simple explanation of the operation of a conventional magnetic amplifier such as shown in Fig. l, to which reference may now be had. Saturable core reactors, as magnetic arnpliiiers are sometimes known, are the actual transformer-like structures such as shown in Fig. l comprised of the power windings 2 and 3, and control windings 8 and 9 connected in. opposition to each other, the windings being wound over conventional laminated iron cores and The load to be controlled, represented by resistor 4, is connected in series with windings 2 and 3 to a suitable alternating current energizing source applied to terminals II. The impedance offered by windings 2 and 3 is controlled from a direct current control voltage applied in series with windings 3 and 9 from terminals I0.

The `alternating current of load windings Il and 3 act in unison whereas the D. C. windings t and 9 are Wound in opposition to each other. In this way although the A. C. voltage appears across the individual D. C. coils 3 and 9, the transformer action thus balances out the fundamental A. C. voltage at terminals I0.

With no direct current applied to terminals l0, the alternating current circuit reduces to the simple case of two inductances in series. Each core will carry an equal pulsating flux, the magnitude and wave shape of the flux being dependent on the magnitude and wave shape of the applied A. C. voltage. If the applied alternating voltage is not so large as to produce a flux of an amplitude exceeding the saturation value each unit will have an innite inductance (assuming the permeability is innite) and no A. C. current will be drawn by load 4.

When a relatively large amount of direct current is applied to terminals I0 the core becomes saturated, the permeability decreases, inductance and consequently the reactance decreases and the A. C. current through windings 2 and 3 increases, allowing more A. C. power to be dissipated in the load Il.

With reference to Figs. 2 and 3 there is illustrated the conventional magnetic amplifier of Fig. 1 having in addition thereto a preferred embodiment of the present invention. The magnetic amplifier shown in Figs. 2 and 3 functions in CFI 4 theory of operation, except as hereinafter explained, similar to the amplifier of Fig. 1, wherein the current across load resistance 4 is directly controlled by the amount of D. C. applied at terminals I 0.

As previously stated, with the use of conventional inexpensive magnetic cores there generally will exist air gaps. The effect of the existence of these gaps is to cause a magnetizing current to flow through the load resistance. Accordingly, with a constant iiow of magnetizing current, the quiescent current or the no load signal output current of the magnetic amplier is never zero. To counteract this undesirable residual magnetizing current iiow, that is to reduce the no load current flow of the magnetic ampliiler to zero, additional coils I3-I4 positioned in adjacent relationship to the load windings 2 and 3, as shown in Fig. 3, are added to the circuit. There is then permitted to ilow in coils I 3--I4 current equal in ampere-turns value to the normal no load magnetizing current ilow of the particular core employed, to balance and cancel the residual magnetizing current.

It is to be understood, of course, that numerous means are known for supplying a small alternating current to core I3-I4. In the preferred embodiment, however, as a mattei' of expediency only, the amount of current flow through coil lli--l is controlled by inductance I2 conveniently connected to the A. C. source. The size of inductance I2 is empirically chosen to permit a current flow through coils I3-I4 of an amount equal in ampere-turns value to the residual magf netizing current. Coils I 3-I 4 are shown as connected to the same source of alternating current that supplies coils 2 and 3.

The advantage of coils I3 and I4 with respect to the performance of the magnetic amplier is best shown by reference to Fig. 4 illustrating the control curves of a magnetic amplifier with various amounts of gaps in the cores with and without the additional Winding of the present invention. The transfer characteristics shown in Fig. 4 are plotted for three nearly equivalent gaps; aero spacing, .002 and .004. The zero spacing, or butt joint, has an apparent spacing of .002 including the magnetizing force for the core itself. Curve 20 is illustrative of a core having a .004" air gap and as seen from the graph the no load current is in the order of .5 average amperes. Curve 23 is illustrative of the amplifier having a core with the same .004 air gap but also having the present invention incorporated therein. It is readily seen from the comparison of curves 20 and 23 that by the incorporation of the present invention the quiescent current (magnetizing current) is reduced from the order of .5 to less than .l average amperes. In a similar manner curves 2| and 24 are illustrative of cores having a .002 air gap, curve 24 with a magnetic ampliiier having the present invention incorporated therein to reduce the quiescent current from approximately .35 average amperes to approximately .05 average amperes. Again curves 22 and 25 are illustrative of a core having a zero gap (apparent .002 gap) wherein the present invention reduces the quiescent current from .22 to .02.

In general the residual magnetizing current is almost completely cancelled. The fundamental frequency can be completely suppressed leaving only the harmonic components which may be somewhat suppressed if the reactance of inductance I2 is designed to duplicate the magnetization curve of the amplifier cores.

It may also be noted in Fig. 4 that the characteristic curves are straightened to more nearly conformto the type of curves ordinarily expected of the materials having a sharp break in their magnetization curves. In the conventional system amplifier gain decreases with the addition of air gaps; although the one to one ratio of control current versus output current is remarkably well preserved when the gap is kept small.

However, it may further be noted from Fig. 4 that the cancellation of the residual magnetizing currents by the present invention does not decrease the amplifier gain for a given gap but to the contrary the amplier gain is increased.

An embodiment of the present invention constructed substantially as the amplifier of Fig. 3 produced the results shown in Fig. 4. In the constructed embodiment of Fig. 3 windings 2 and 3 have 400 turns each, windings I3 and I4, 40 turns each; inductance I2 nine times the inductance of windings I3 and I4; and control coils 8 and 9, 400 turns of No. 17 formvar wire. Hypersil type C-94 cores (0,007" laminations) with ik x 1" cross section were used for cores 5 and 6. The knee of the saturation curve was reached at approximately 95 volts (R. M. S. 60 cycles).

Although certain preferred embodiments of the present invention are shown it is to be expressly understood that modications may be made thereof without departing from the true spirit and sco-pe of the invention.

The invention described herein may .be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. A magnetic amplier comprising a pair of. saturable magnetic cores having respective airgaps therein, an alternating-current load winding and a direct current control winding wound on each of said cores, the load windings being connected in series and the control windings being connected in series opposition, a low inductance tertiary winding wound on each of said cores for reducing to a minimum the magnetizing current which ows through said load windings, said tertiary windings being connected in series and continuously energized during ampliiier operation, and a relatively high inductance con- 50 nected in series with said tertiary windings.

2. A magnetic amplifier comprising a pair of saturable magnetic cores having respective airgaps therein, an alternating current load winding `and a direct current control winding wound on each of said cores, the load windings being connected in series and the control windings being connected in series opposition, a tertiary Winding wound on each of said cores, said tertiars7 windings being continuously energized during amplier operation, and current control means coupled to said tertiary windings for maintaining the ampere-turns thereof substantially equal to the ampere-turns of said alternating-current load windings respectively.

3. A magnetic amplifier comprising a pair of saturable :magnetic cores having respective airgaps therein, and alternating-current load winding and a direct current control winding wound on each of said cores, the load windings being connected in series and the control windings being connected in series opposition, and means for reducing to a minimum the no load magnetizing current which flows through said alternatingcurrent windings including a tertiary winding wound on each of said cores, said tertiary windings being connected in series and continuously energized during amplier operation, and current control means coupled in series with said tertiari7 windings for limiting the ampere-turns thereof to a value substantially equal to the ampere-turns of said alternating-current windings at no load.

4. A magnetic amplifier comprising a pair of satura'ble magnetic cores having respective airgaps therein, a plurality of windings wound on each of said cores, said plurality of windings consisting of an alternating-current load winding, a direct-current control winding and a tertiary winding, the load windings being connected in series and the control windings being connected in series opposition, the tertiary windings being connected in series and continuously energized during amplier operation, and inductance means in series with said tertiary windings for limiting the ampere-turns thereof to a Value substantially equal to the ampere-turns of said altermating-current windings at no load.

ROBERT A. RAMEY.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,453,470 Steinitz Nov. 9, 1948 2,486,343 Taylor Oct. 25, 1949 

